Important Bird Areas

Mount Hamilton Range (East Diablo Range)

California

This area encompasses the eastern slopes of the Coast Range separating the east San Francisco Bay Area and the Central Valley. A natural intersection of habitats - the hot, arid valley and the cool, mesic coast - support a number of interesting plants and animals that do not co-occur elsewhere. Practically all ornithological investigation has been conducted along the few public roads through the area, focusing on four areas: Corral Hollow, Mines Rd., San Antonio Valley and Del Puerto Canyon Corral Hollow Rd. connects the towns of Tracy in the Central Valley with Livermore, and is located in a prominent low pass through the Coast Range. Though the area is dominated by private ranchland, there are several public holdings, including Del Valle Regional Park (west of Mines Rd.), Frank Raines Regional Park (Del Puerto Cyn. Rd.) and tiny Corral Hollow Ecological Area. Mines Rd. runs north-south through the entire area for about 40 miles, and Del Puerto Cyn. intersects the south end of Mines Rd. within the San Antonio Valley, and then heads east, dropping into the Central Valley southwest of Modesto.

Ornithological Summary

The savannah-covered hills near Livermore have been found to support one of the highest densities of breeding Golden Eagles in the state, with at least 44 territories (http://www2.ucsc.edu/scpbrg/eagles.htm). The chaparral in this area supports breeding populations of sage scrub and arid country species reminiscent of southern California, such as Greater Roadrunner, Costa's Hummingbird, Cassin's Kingbird, Bell's Sage Sparrow, Black-chinned Sparrow and Lawrence's Goldfinch (Edwards 2000). Riparian obligates such as Yellow-breasted Chat breed in small, willow-filled drainages, and even Least Bell's Vireo apparently occurred in the riparian draws in Corral Hollow (Grinnell and Miller 1944), and may yet return given recent successes in southern California. Long-eared Owl and Lewis' Woodpecker, both local in the region, have bred in the oak savannah here. At higher elevations, Coulter Pine forest dominates, which supports breeding montane birds such as Olive-sided Flycatcher and Yellow-rumped Warbler (fide Steve Glover), contributing to the exceptional breeding diversity of the area. The patches of grassland within the Important Bird Area, especially near Livermore and along the eastern base of the Important Bird Area, still support breeding populations of Northern Harrier, White-tailed Kite (including communal winter roosts, Small 1994), Burrowing Owl (one of the few remaining Bay Area locales), Loggerhead Shrike, Grasshopper Sparrow, Tricolored Blackbird and in winter, good numbers of Ferruginous Hawk. The area boasts an exceptional diversity of reptiles and amphibians, and the Livermore grasslands, long isolated from the Central Valley, support several sensitive species such as the federally threatened Red-legged Frog. About 20 pair of Prairie Falcons are believed to breed in the Diablo Range, mainly in the east (fide Steve Glover), and a pair of Bald Eagles breeds at Del Valle Reservoir (Alameda County) just west of Mines Rd.

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Conservation Issues

While the habitat in the center of this Important Bird Area is probably secure simply because of the ruggedness of the terrain, that on its borders, especially the grassland expanses around Livermore and at the edge of the Central Valley, remain particularly threatened by development. Corral Hollow, renowned for its rich and unique reptile and amphibian community, is threatened by a nearby OHV park (The Nature Conservancy 1998).

Ownership

The area is dominated by private ranchland but there are several public holdings, including Del Valle Regional Park (west of Mines Rd.), Frank Raines Regional Park (Del Puerto Cyn. Rd.) and tiny Corral Hollow Ecological Area.

Habitat

The savannah-covered hills near Livermore have been found to support one of the highest densities of breeding Golden Eagles in the state. The chaparral in this area supports breeding populations of many species and sage scrub and arid country species reminiscent of southern California. Riparian obligates such as Yellow-breasted Chat breed in small, willow-filled drainages. Long-eared Owl and Lewis? Woodpecker, both local in the region, have bred in the oak savannah here. At higher elevations, Coulter Pine forest dominates. There are also patches of Livermore grasslands, long isolated from the Central Valley.